In level measurement applications, pulse-echo ranging devices, also known as time-of-flight ranging devices, are commonly used for determining the distance to a target object (e.g. reflective surface of a material in a container) by measuring how long after transmission of a burst of energy pulses the reflected pulses or echoes are received. Such devices typically use ultrasonic pulses or pulsed radar or microwave signals.
Pulse-echo acoustic ranging devices generally include a transducer and a signal processor. The transducer serves the dual role of transmitting the energy pulses and receiving the reflected energy pulses or echoes. An echo profile is generated from the received energy pulses by amplifying, filtering and envelope shaping, wherein in some point an analog-to-digital conversion is performed. Echo pulses are identified in the digital echo profile by a signal processor, and the distance or range of the target is calculated based on the transmit times of the transmitted energy pulses and the identified echo pulses. The calculated distance or range is then transmitted via a communication network to a process control system using a communications protocol such as analog 4-20 mA, HART, PROFIBUS or FOUNDATION Fieldbus.
When measurements at different points of the same surface of, e.g., a bulk material or at different locations or sites are required, one complete device is needed for each measurement, which can be very expensive.